1. Technical Field
The present invention relates to the cooling of vacuum devices. More particularly, the present invention relates to a method and apparatus for cooling a thermal load in a vacuum device that results from such factors as gas flow from a vacuum chamber to an exhaust pump.
2. Description of the Prior Art
A vacuum pump, such as the cryopump 3 shown in FIG. 1, is used in the prior art to evacuate a process gas from a vacuum chamber 2 and thereby maintain a stable, selected vacuum in the interior of the vacuum chamber, while constantly purging the chamber of expended process gases. Because the cryopump requires specific operating conditions, it is usually necessary to reduce the thermal load on cryopump. For example, heat transfer to the cryopump from the process gas may be prevented by a heat shield 41, which absorbs heat from the gas, as well as any radiation heat. The heat shield 41 is cooled by a flow of cooling water, thereby increasing the heat shield cooling efficiency.
It is necessary to position a cooling pipe 42 within the vacuum chamber to provide a flow of coolant to cool the heat shield 41 because the heat shield is located within the vacuum chamber. Consequently, it is necessary to provide openings in the outer wall of the vacuum chamber to allow the cooling pipe 42 to be admitted into the vacuum chamber. The openings must be airtight under vacuum conditions and therefore must include a seal 43 to maintain the vacuum within the vacuum chamber interior. Because the vacuum chamber is used for extended periods of time, the seal 43 is subjected to repeated stress and is easily damaged, such that ambient air leaks through the openings, preventing maintenance of a vacuum in the vacuum chamber.
Because a seal 43 is needed, the vacuum chamber configuration can become complicated. For example, even when it is only necessary to repair the vacuum chamber heat shield 41 and cooling pipe 42, it is still necessary to exchange the entire vacuum chamber. Furthermore, if the cooling pipe is damaged, then cooling water may leak into the vacuum chamber, damaging both the chamber and any work in progress.
It would be advantageous to provide a simple, high integrity system for cooling a vacuum system that did not suffer from the above limitations.